it's afaik currently tracking slightly above the PS3 that did 10.5m lt and MHW should give it another good stimulus, but with the Switch very likely dominating the market from here on out even reaching 10m+ will be a tough/long battle depending on how many JPN 3rd parties go straight to NSW (and even PS4/NSW games could harm PS4 sales)
for 15m the PS4 would need an epic killer app that amplifies hw sales for months to come and with MH there is a small chance for that to happen there .. other than MHW there isn't much on the horizon that could do this especially as pretty much all traditional medium to big jpn 3rd party franchises already had their chance (still FF7R maybe?, total mega dark horse being Gran Blue?)
Pretty much this. The PS4 is going to have to sell on price and just consistent 3rd game releases at this point. The biggest franchises in JP are Nintendo IP's, Final Fantasy, Dragon Quest, Yokai Watch, and Monster Hunter, and PS4 already had a FF and DQ game, which boost sales, but not where they needed. Monster Hunter could be big for them, but it's questionable if it's going to be big enough to really blow PS4 sales up there.
JP cares about Pokemon, Animal Crossing, Mario Kart, Smash Bros., Mario, Splatoon, etc... too much, and everyone of those games belong to Nintendo which is why JP belong to Nintendo, specifically their handheld division.
By all means PS4 should be doing much better than PS3 in JP, and it's not. Hopefully it does pick up and sales shoot pass 10m, but if not it truly means console gaming is practically dead in JP.